The persistence of lead from past gasoline emissions and mining drainage in a large riparian system: Evidence from lead isotopes in the Sacramento River, California

Lead concentrations and isotope ratios measured in river water colloids and streambed sediment samples along 426 km of the Sacramento River, California reveal that the influence of lead from the historical mining of massive sulfide deposits in the West Shasta Cu-mining district (at the headwaters of the Sacramento River) is confined to a 60 km stretch of river immediately downstream of that mining region, whereas inputs from past leaded gasoline emissions and historical hydraulic Au-mining in the Sierra Nevadan foothills are the dominant lead sources in the remaining 370 km of the river. Binary mixing calculations suggest that more than 50% of the lead in the Sacramento River outside of the region of influence of the West Shasta Cu-mining district is derived from past depositions of leaded gasoline emissions. This predominance is the first direct documentation of the geographic extent of gasoline lead persistence throughout a large riparian system (>160,000 km²) and corroborates previous observations based on samples taken at the mouth of the Sacramento River. In addition, new analyses of sediment samples from the hydraulic gold mines of the Sierra Nevada foothills confirm the present-day fluxes into the Sacramento River of contaminant metals derived from historical hydraulic Au-mining that occurred during the latter half of the 19th and early part of the 20th centuries. These fluxes occur predominantly during periods of elevated river discharge associated with heavy winter precipitation in northern California. In the broadest context, the study demonstrates the potential for altered precipitation patterns resulting from climate change to affect the mobility and transport of soil-bound contaminants in the surface environment.     

Geochemistry, petrology and ages of the lunar meteorites Kalahari 008 and 009: New constraints on early lunar evolution

Kalahari 008 and 009 are two lunar meteorites that were found close to each other in Botswana. Kalahari 008 is a typical lunar anorthositic breccia; Kalahari 009 a monomict breccia with basaltic composition and mineralogy. Based on minor and trace elements Kalahari 009 is classified as VLT (very-low-Ti) mare basalt with extremely low contents of incompatible elements, including the REE. The Lu-Hf data define an age of 4286 ± 95 Ma indicating that Kalahari 009 is one of the oldest known basalt samples from the Moon. It provides evidence for lunar basalt volcanism prior to 4.1 Ga (pre-Nectarian) and may represent the first sample from a cryptomare. The very radiogenic initial ¹⁷⁶Hf/¹⁷⁷Hf (εHf = +12.9 ± 4.6), the low REE, Th and Ti concentrations indicate that Kalahari 009 formed from re-melting of mantle material that had undergone strong incompatible trace element depletion early in lunar history. This unusually depleted composition points toward a hitherto unsampled basalt source region for the lunar interior that may represent a new depleted endmember source for low-Ti mare basalt volcanism. Apparently, the Moon became chemically very heterogeneous at an early stage in its history and different cumulate sources are responsible for the diverse mare basalt types.Evidence that Kalahari 008 and 009 may be paired includes the similar fayalite content of their olivine, the identical initial Hf isotope composition, the exceptionally low exposure ages of both rocks and the fact that they were found close to each other. Since cryptomaria are covered by highland ejecta, it is possible that these rocks are from the boundary area, where basalt deposits are covered by highland ejecta. The concentrations of cosmogenic radionuclides and trapped noble gases are unusually low in both rocks, although Kalahari 008 contains slightly higher concentrations. A likely reason for this difference is that Kalahari 008 is a polymict breccia containing a briefly exposed regolith, while Kalahari 009 is a monomict brecciated rock that may never have been at the surface of the Moon.Altogether, the compositions of Kalahari 008 and 009 permit new insight into early lunar evolution, as both meteorites sample lunar reservoirs hitherto unsampled by spacecraft missions. The very low Th and REE content of Kalahari 009 as well as the depletion in Sm and the lack of a KREEP-like signature in Kalahari 008 point to a possible source far from the influence of the Procellarum-KREEP Terrane, possibly the lunar farside.     

A strong temperature effect on U/Ca in planktonic foraminiferal carbonates

Three planktonic foraminiferal species Globigerina bulloides, Neogloboquadrina pachyderma (d), and Globorotalia inflata collected from core-tops spanning 35° to 65°N in the North Atlantic were used for U/Ca and Mg/Ca and foraminiferal shell weight analyses. Except for U/Ca in G. bulloides calcified under warm conditions (>∼13 °C), U/Ca ratios in all three studied species increase with decreasing latitude and show strong positive correlations with Mg/Ca ratios. A dissolution effect on planktonic U/Ca is suggested by decreased shell weight and U/Ca and Mg/Ca ratios for shells from very deep water depth (>4.4 km) along the latitudinal transect. G. bulloides from down core samples in the North Atlantic show low U/Ca ratios during the last glacial and high ratios during the Holocene, similar to the Mg/Ca evolution trend. In general, our data indicate that the U incorporation into planktonic foraminiferal carbonates is strongly influenced by calcification temperature, although U/Ca in G. bulloides may be affected by seawater carbonate ion concentration under warm conditions and/or other factors.     

Models in geography revisited

Agent based models (ABMs) have many applications, and illustrate a rapidly developing field of enquiry, spanning both the physical-mathematical and human-social sciences. ABMs are seen as most appropriate in situations where decisions or actions are distributed around particular locations, and in which structure is viewed as emergent from the interaction between individuals. ABMs may be used either as representational devices, to reproduce the patterns observed or desired in the system of interest, or as foundational tools contributing to the development of social or economic theory. The role and status of models and modelling is itself an instantiation of a wider debate concerning representation and explanation. Today, a case can be made that the nature of explanation and the use of scientific interpretation reflect much less definite and exclusive positions and permit more diverse approaches than hitherto. The underlying proposition of this commentary is, therefore, that the time is right for a positive application of ABMs within the discipline of geography, and for a rediscovery and reappraisal of the richness and depth of insight in the model-building enterprise more generally. First, the context for ABM development and application is set with reference to the agency-structure debate. Second, some aspects of the heritage of models in geography is presented, based upon reviews of two benchmark publications bearing that title. Next, some of the most significant characteristics, uses, potentials and limitations of ABMs, are reviewed. Finally, some constructive ways forward are suggested, as informed by theory and method from the interpretative social sciences.     

The posthumous tectonics and mechanism of exhumation of granitic plutons: The case of the Transbaikal region and the Tien Shan

The study of granitic plutons of the Baikal Highland and the Tien Shan has made it possible to establish new features of their posthumous (after incorporation into the consolidated Earth’s crust) structural reworking and to understand the implications of the cataclastic flow for the exhumation of the crystalline basement in the studied regions. It is shown that granitic plutons undergo appreciable structural transformation at the stages of tectonic reactivation that is significantly separated in time from the moment of formation of plutons as geological bodies. The 3D cataclastic deformation is the main mode of structural reworking of granitic plutons, while the cataclastic flow is the main form of their mobility. Newly recognized slice structures characterize the volumetric deformation of granites.     

Lateral structural variability in zone of eocene island-arc-continent collision,Kamchatka

The lateral variability of structural elements in the collision zone of the Cretaceous-Paleocene Achaivayam-Valagin island arc with the northeastern Asian margin is considered. The similarity and difference of Eocene collision structural elements in the north and the south of Kamchatka are shown. In northern Kamchatka, the continent-arc boundary is traced along the Lesnaya-Vatyn Thrust Fault, which completed its evolution about 45 Ma ago. The thin, near-horizontal allochthon of this thrust, composed of island-arc rocks, overlies the deformed but unmetamorphosed terrigeneous sequences of the Asian margin. The general structure of this suture in the Kamchatka Isthmus and southern Koryakia is comparable with the uppermost subduction zone, where a thin lithospheric wedge overlaps intensely deformed sediments detached from the plunging plate. In southern Kamchatka (Malka Uplift of the Sredinny Range), the arc-continent collision started 55–53 Ma ago with thrusting of island-arc complexes over terrigenous rocks of continental margin. However, the thickness of the allochthon was much greater than in the north. Immediately after this event, both the autochthon and lower part of allochthon were deformed and subsided to a significant depth. This subsidence gave rise to metamorphism of both the autochthon (Kolpakov and Kamchatka groups, Kheivan Formation) and lower allochthon (Andrianovka and Khimka formations). The anomalously fast heating of the crust was most likely related to the ascent of asthenospheric masses due to slab breakoff, when the Eurasian Plate was plunging beneath the Achaivayam-Valagin arc.     

Synchronism in compression of the lithosphere in the central Atlantic and Western Tethys at the Tortonian-Messinian transition

The structure of anomalously uplifted areas in transverse ridges of the Vema, S o Paulo, and Romanche fracture zones is considered. It is concluded that their formation and eventual development in the present-day structure of the central Atlantic bottom proceeded during two stages. The first stage that corresponds to a short period at the Tortonian-Messinian transition (10 Ma ago) was marked by transportation of deep-seated rocks into the upper part of the lithosphere along thrust faults with mass motion in the meridional direction along the axis of the Mid-Atlantic Ridge. The second stage was characterized by contrasting highamplitude vertical movements from 10 to 3 Ma ago. It is suggested that near-meridional compression in the domains surrounding the Western Tethys in the Tortonian-Messinian resulted in deformation of the upper lithosphere within large transform fracture zones of the central Atlantic. The deformation that occurred 10 Ma ago was a manifestation of the global neotectonic epoch of the Earth.     

Sorption of Ni on Na-rectorite studied by batch and spectroscopy methods

Sorption of Ni²⁺ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni²⁺ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni²⁺ at low pH values, whereas no drastic effect of FA/HA on Ni²⁺ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni²⁺ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni²⁺ at different temperatures. The thermodynamic data (ΔH⁰, ΔS⁰, ΔG⁰) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni²⁺ on rectorite was spontaneous and endothermic. The sorption and species of Ni²⁺ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni²⁺ mainly occurred on the surface and at the edge position of Na-rectorite.     

Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh,India, Vietnam,and Nepal

One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.     

Biofacies analysis of Upper Cretaceous deposits in the Ust-Yenisei region: Implications of palynomorphs

The results of palynomorph biofacies analysis in the Upper Cretaceous deposits of the Ust-Yenisei region are presented. The established facies confinement and indicative features of separate palynomorph groups are used, along with identified dinocyst morphotypes and taxa, in paleogeographic reconstructions. Seven palynomorph associations characterizing continental, coastal-marine, shallow-and deep-water facies are distinguished based on quantitative proportions between morphological groupings and individual taxa. As boundaries between distinguishable biostratigraphic and facies subdivisions do not coincide, dinocysts were likely insignificantly dependent in distribution on facies in the West Siberian epicontinental basin at least. On the other hand, distribution trends of particular dinocyst morphotypes and other microphytofossils are correlative with transgressive-regressive cycles and can be used for reconstruction of paleoenvironments.